The proposed project permits completion of a long-term research program that was begun in 1974 and that will ultimately (1980) yield separable but interlocking investigations. The program uses a new approach, the Representative Case Method; it employs directed interviews and a comprehensive battery of standard and special tests to examine nine men, carefully selected in each of five categories: users/abusers of cocaine; users/abusers of amphetamines; users/abusers of opiates; users/abusers of barbiturates; and men who are not involved in illicit drug use. Data from each participant-expert will be analyzed separately. Comparisons will also be carried out among individuals, within and across categories. Aggregating the data will yield four groups of drug users/abusers, to be compared to each other and with the control group. Additional analyses will compare the aggregated group who prefer stimulants (cocaine and amphetamines) with the group who prefer depressants (opiates and barbiturates) and with non-abusers. Finally, the aggregated group of all drug users/abusers will be compared with the control group of non-abusers. Support is required for completion of data collection in the last two categories and for the final integrative analysis and reporting of results from all modules.